Topic: Hesitating at full throtle

[hozer]

Hello, I have a 97 4 cyl., everything stock except for 4" lift and 33" BFG's.  The other day I took the squirrels out for some excercize and I pushed the  pedal to the floor. The thing started to hesitate and buck. I let off it ran fine tried it again and it did the same thing. It's got a fairly fresh tune up so, I don't believe it to be spark or wires. Any suggestions on what it may be would  greatly be appreciated. I live in upstate NY and the road salt will be getting dumped soon, so wash wax and cover for the winter will be next weekends project. Long winters so time to work on it. Thanks

[hozer]

Sorry, I posted in the wrong forum.

[DDUBYJ]

It supposed to do that, its a REV LIMITER, so you dont over rev the engine and blow a squirrel through the hood.

        i use mine all the time, it wont hurt it. 

[dwtaylorpdx]

Hmm. I've never found the rev limiter, and I've pushed mine over 7000 many times.
Wonder if the OBD1 computers did not have one?

I have had the symptom described when I had a bad spot in a TPS.

Dave

[sharpxmen]

Hmm. I've never found the rev limiter, and I've pushed mine over 7000 many times.
Wonder if the OBD1 computers did not have one?

I have had the symptom described when I had a bad spot in a TPS.

Dave

mine has a rev limiter and pretty much any car with an ECU controlled ignition has one. Even the old style distributors have a mechanical rev limiter (on the dist rotor there's a weight on a spring that is shorting out the spark once you get too high in rpm - centrifugal based), i believe that any decent car manufacturer started to have them on since 1980 if not earlier.

@DDUBYJ: he is probably having this issue before hitting the rev limit

could be like Dave said the TPS but i think that would throw a code (check engine light) - i had the same thing once but the CEL came on and i had a code that was TPS malfunction or something like that. MAP malfunction can also cause that problem a(although they don't fail as often or very rarely). Fuel pressure dropping due to faulty pump, bad pressure regulator or plugged filter can also have the same symptom. Can be a spark related issue as well (dist, cap, rotor wires, plugs, coil, crank sensor).

I guess you'll have to start testing and verify all these. If there's a check engine light get the code first and see what it says, could be that the answer is right there.

[Jeffy]

The Rev limited is supposed to be around 5800RRM but I think the PCM's a bit stupid and ignores it if you downshift.

I'm wonder if the OP is lugging the engine.  What are your RPM's when you're trying to floor it and what gear are you in?

[dwtaylorpdx]

I've never seen a rev limiter on an American car that's integrated into the distributor.
Many have advance weights, but for the most part It would be in the ECU for EFI.
The only distributor Rev Limiter I've seen is in Marrelli in Porsche, Fiat, Alpha, and
Ferrari and they do have a patent on it, it works as you describe. GM HEI sort of has
one, the thing just malfunctions at about 6800 and quits firing. Its a feature...

As I pointed out, my engine gets time over 6000 all the time and peaks at 7000 in the sand.
There has yet to be any sign that it has a limiter... Of course maybe it has a override like being
at WOT on the floor? Or maybe its just been screwed up since day 1 when I bought it..

Now the rental car I had a few weeks ago from GM had paddle shifters and I did manage to fully
hit the limiter in that car 

Bad TPS throwing a code, Mine did, it threw an O2 sensor code.  luckily I
tested the O2 and did not just buy one. And the symptom was a harsh misfire but if I
pushed through it to WOT it was fine. It had a dead spot around 80% throttle.

Interesting little beggars the jeep, no 2 alike 

Dave

[sharpxmen]

I've never seen a rev limiter on an American car that's integrated into the distributor.
Many have advance weights, but for the most part It would be in the ECU for EFI.
The only distributor Rev Limiter I've seen is in Marrelli in Porsche, Fiat, Alpha, and
Ferrari and they do have a patent on it, it works as you describe. GM HEI sort of has
one, the thing just malfunctions at about 6800 and quits firing. Its a feature...

bmw has them too, so did opel, audi and renault and the ones you mentioned. The ones with EFI also cut off the gas to prevent autoignition. When you downshift (like Jeffy mentioned) the engine will overrev but the spark/gas will be out until you go below the limiter (or at least that's what is supposed to do by design).
It's surprising that yours does not cut out, not sure what to think about that other than the PCM being reprogrammed but that's quite unlikely (I looked and never found a programmer for the 91-95 Jeep PCM) but i've seen things more strange than that - i did manage to hit the limiter a few times on mine when i was daydreaming and going uphill, but usually i stay away from the red zone on the tach. I wouldn't think that engine was ever designed to go over 6000 - cast pistons, single row cam chain + at that rpm your power goes down unless you have a perf cam and intake.

EDIT: i had a Dakota 5.9 R/T, and that thing on top of the rev limiter had a speed limiter as well - it's been a long time but if i recall correctly was cutting you out at 190kph (120mph or so) - i thought i busted the engine as it cut out, really not a good speed to get freaked out at :)

[chardrc]

im premember yjmechanic talked about how he could never find the rev limiter in his yj.. so the rev-limiter not happening seems to be something that does "happen"

http://4bangerjp.com/forums/index.php/topic,314.45.html

[sharpxmen]

im premember yjmechanic talked about how he could never find the rev limiter in his yj.. so the rev-limiter not happening seems to be something that does "happen"

http://4bangerjp.com/forums/index.php/topic,314.45.html

could be that some of the PCMs came with a different code (firmware) revision out of the factory for some reason - some might have been updated during warranty as well.

[jfrabat]

could be that some of the PCMs came with a different code (firmware) revision out of the factory for some reason - some might have been updated during warranty as well.

When I read yjmechanics comment, I took mine for a spin...  I got over 6K RPMs and no limiter (have had them in previous cars, so I have seen them at work, just not on my YJ)

[dwtaylorpdx]

bmw has them too, so did opel, audi and renault and the ones you mentioned. The ones with EFI also cut off the gas to prevent autoignition. When you downshift (like Jeffy mentioned) the engine will overrev but the spark/gas will be out until you go below the limiter (or at least that's what is supposed to do by design).
It's surprising that yours does not cut out, not sure what to think about that other than the PCM being reprogrammed but that's quite unlikely (I looked and never found a programmer for the 91-95 Jeep PCM) but i've seen things more strange than that - i did manage to hit the limiter a few times on mine when i was daydreaming and going uphill, but usually i stay away from the red zone on the tach. I wouldn't think that engine was ever designed to go over 6000 - cast pistons, single row cam chain + at that rpm your power goes down unless you have a perf cam and intake.

EDIT: i had a Dakota 5.9 R/T, and that thing on top of the rev limiter had a speed limiter as well - it's been a long time but if i recall correctly was cutting you out at 190kph (120mph or so) - i thought i busted the engine as it cut out, really not a good speed to get freaked out at :)

Well I'm running an engine built for the RPM level now...  
Hyperutectic coated pistons, double row chain, upgraded valve springs, cam, race quality balance, etc.

What I wonder is if even the dealer can flash a 94, when I had mine in the shop trying  
to chase a bug, the tech was a pretty sharp guy and he mentioned that he had never
found a way to change the programming. I know I opened the ECU one time and it was potted
so you could not easily remove the flash ram.

My 95 BMW is speed and rev limited, I've hit both...  
Its limited to 116 according to the BMW manual. As are all the US BMW cars.

Couple years ago I read an article about a guy trying to set a speed record with a mustang at Bonneville.
He mentioned there being 5 separate speed limiters in the car including 2 rev limiters. they ended up doing
a bunch of weird stuff and getting Ford Motorsports to fedex a race ECU to Utah...

Corvette charges to remove the speed limiter and flags the display in the dash if you do it...

Dave

[sharpxmen]

When I read yjmechanics comment, I took mine for a spin...  I got over 6K RPMs and no limiter (have had them in previous cars, so I have seen them at work, just not on my YJ)

i can't be certain but i think when I hit mine at over 6k - Jeffy said it's 5800 so i'm not sure now. one thing i am sure of is that i wouldn't go that high again deliberately but by accident i might, if it happens i'll report back (well, need to get the Jeep back on the street first)

[Jeffy]

I've taken my engine to 6K by accident and didn't notice the rev. limiter kick in.  The engine was screaming but the RPM's were constant and not dancing on the limiter.

[hozer]

It'a an automatic and, about a year or so ago, I was having an issue with the " COST YOU MORE MONEY" ck engine light being on. Well that turned out to be a wire issue that I fixed. I did however take it to the local  Jeep stealership and they flashed the computer and did some updates in it. That may be the reason why I hit the rev limiter this time. I know prior to that I don't think I ever hit it.
   Thanks for all the input.